Aluminum-iron-zirconium alloys

ABSTRACT

Aluminum-Iron-Zirconium alloys that exhibit improved electrical and mechanical properties.

The present application claims the benefit of the filing date of U.S.Ser. No. 62/241,543, filed 14 Oct. 2015.

TECHNICAL FIELD

The present disclosure generally relates to improvedaluminum-iron-zirconium alloys that exhibit improved electrical andmechanical properties.

BACKGROUND

It is known to use aluminum or aluminum alloys in many applications as aconsequence of alumninum's relatively low density and generallysatisfactory electrical and mechanical properties. However, aluminum andcertain aluminum alloys suffer from various detriments that impair theiruse in some applications. For example, certain aluminum conductors cansuffer from time consuming and energy-intensive processing steps and canexhibit poor electrical or mechanical properties when used as aconductive element or when used at elevated temperatures. It wouldtherefore be desirable to create an improved aluminum alloy that iseasier to produce while also offering improved electrical and mechanicalproperties.

SUMMARY

In accordance with some embodiments, an aluminum alloy comprisesaluminum, iron, zirconium, and an inoculant; wherein the aluminum alloycomprises a plurality of precipitates, and the plurality of precipitatesare present in the aluminum alloy at a density of about 10²¹precipitates per m³ or more. In some embodiments, the inoculantcomprises one or more of tin, indium, antimony, and magnesium. In someembodiments, the aluminum alloy further comprises silicon. In someembodiments, the inoculant comprises one or more of zinc, gallium,germanium, lead, arsenic, and bismuth. In some embodiments, theinnoculent comprising one or more of zinc, gallium, germanium, lead,arsenic, and bismuth, comprises about 0.01% to about 0.2% of thealuminum alloy by weight. In some embodiments, the inoculant comprisesat least one Group 3A, 4A, 5A metal or metalloid. In some embodiments,the iron comprises about 0.1% to about 1% of the aluminum alloy byweight. In some embodiments, the iron comprises about 0.3% to about 0.7%of the aluminum alloy by weight. In some embodiments, the zirconiumcomprises about 0.1% to about 0.5% of the aluminum alloy by weight. Insome embodiments, the inoculant comprises about 0.01% to about 0.2% ofthe aluminum alloy by weight. In some embodiments, the inoculantcomprises tin, the aluminum comprises about 99% of the aluminum alloy byweight, the iron comprises about 0.3% to about 0.5% of the aluminumalloy by weight, the zirconium comprises about 0.2% to about 0.4% of thealuminum alloy by weight, and the tin comprises about 0.01% to about0.2% of the aluminum alloy by weight. In some embodiments, the aluminumalloy further comprises silicon, wherein the silicon comprises about0.01% to about 0.2% of the aluminum alloy by weight. In someembodiments, the aluminum comprises about 99% of the aluminum alloy byweight, the iron comprises about 0.3% to about 0.5% of the aluminumalloy by weight, the zirconium comprises about 0.2% to about 0.4% of thealuminum alloy by weight, and the inoculant comprises about 0.01% toabout 0.2% of the aluminum alloy by weight. In some embodiments, theinoculant comprises tin, the aluminum comprises about 99% of thealuminum alloy by weight, the iron comprises about 0.55% of the aluminumalloy by weight, the zirconium comprises about 0.34% the aluminum alloyby weight, and the tin comprises about 0.1% of the aluminum alloy byweight. In some embodiments, the inoculant comprises tin, the aluminumcomprises about 99% of the aluminum alloy by weight, the iron comprisesabout 0.4% to about 0.5% of the aluminum alloy by weight, the zirconiumcomprises about 0.25% to about 0.3% of the aluminum alloy by weight, andthe tin comprises about 0.05% to about 0.1% of the aluminum alloy byweight. In some embodiments, the aluminum alloy further comprisessilicon, wherein the silicon comprises about 0.04% of the aluminum alloyby weight; the inoculant comprises tin, and the tin comprises about0.07% of the aluminum alloy by weight; the aluminum comprises about 99%of the aluminum alloy by weight; the iron comprises about 0.43% of thealuminum alloy by weight; and the zirconium comprises about 0.27% of thealuminum alloy by weight. In some embodiments, the plurality ofprecipitates has an average diameter of about 20 nm or less. In someembodiments, the plurality of precipitates has an average diameter ofabout 10 nm or less. In some embodiments, the plurality of precipitateshas an average diameter of about 3 nm to about 7 nm.

In some applications, a cable includes at least one conductive elementformed from an aluminum-zirconium alloy. The aluminum-zirconium alloyfurther includes an inoculant. The at least one conductive element hasan ultimate tensile strength of about 120 MPa or more after heat agingfor 48 hours at 400° C. and exhibits a stress relaxation time to reachabout 85% of an initial stress that is about 2 times longer in durationthan a similar aluminum-zirconium alloy formed without an inoculant whenmeasured in accordance to ASTM E328.

In some applications, a conductive element for a cable includes analuminum-zirconium alloy. The aluminum-zirconium alloy has an ultimatetensile strength of about 140 MPa or more after heat aging for 48 hoursat 400° C. and exhibits a stress relaxation time to reach about 85% ofan initial stress that is about 2 times longer in duration than asimilar aluminum-zirconium alloy formed without an inoculant whenmeasured in accordance to ASTM E328. The aluminum-zirconium alloyincludes about 99% by weight aluminum, about 0.3% to about 0.5% byweight iron, about 0.2% to about 0.4% by weight zirconium, and about0.01% to about 0.2% by weight tin.

In some applications, a method of making a conductive element for acable includes continuously casting an as-cast shape from analuminum-zirconium alloy, hot rolling the as-cast shape to form a redrawrod, drawing the redraw rod into a wire, and annealing the wire to forma conductive element. The aluminum-zirconium alloy further includes aninoculant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a graph illustrating the room temperature stressrelaxation times of an improved aluminum-zirconium alloy according toone embodiment, and the room temperature stress relaxation time of aconventional aluminum-zirconium alloy.

FIG. 2 depicts a graph illustrating the room temperature fatigueproperties of an improved aluminum-zirconium alloy according to oneembodiment, and the room temperature fatigue properties of aconventional 8000-series aluminum alloy.

FIG. 3 depicts a graph illustrating the results of a 20 mil (0.508 mm)shear test demonstrating the bonding performance of an improvedaluminum-zirconium alloy according to one embodiment.

DETAILED DESCRIPTION

Aluminum alloys exhibiting improved conductivity and mechanicalproperties at elevated temperatures can provide numerous benefits whenused as conductive elements in cables. In certain embodiments, animproved aluminum alloy exhibiting such features can be analuminum-zirconium alloy including an inoculant that increases thediffusivity of zirconium in the aluminum. According to certainembodiments, examples of suitable inoculants can include any metal ormetalloid that lowers the activation energy required for diffusion in anα-Al matrix as compared to the activation energy required for diffusionin an α-Al matrix free of an inoculant. Non-limiting examples of suchinoculants can include Group 3A, Group 4A and Group 5A metal andmetalloids as well as zinc. For example, suitable inoculants that canincrease the kinetics of zirconium diffusion in an α-Al matrix caninclude tin, indium, antimony, magnesium, zinc, gallium, germanium,lead, arsenic, bismuth, and in combination with other inoculants,silicon in certain embodiments.

Without being bound by theory, it is believed the inclusion of asuitable inoculant in an aluminum-zirconium alloy increases thediffusivity of the zirconium in the aluminum alloy which causes bothsupersaturation of zirconium and a decrease in the precipitationtemperature of zirconium. As can be appreciated, such diffusivity canallow for precipitation of a large number density of relatively smallprecipitates using lower temperatures and/or time than a similaraluminum-zirconium alloy without such an inoculant. For example, heataging of an aluminum-zirconium alloy including an inoculant can beperformed at lower temperatures for constant heat aging time than asimilar aluminum-zirconium alloy free of an inoculant (e.g., attemperatures about 45° C. lower in certain embodiments) and/or for ashorter duration than a similar aluminum-zirconium alloy free of aninoculant for constant heat aging temperature (e.g., for durations about50 hours shorter according to certain embodiments). As can beappreciated, an aluminum-zirconium alloy with a larger quantity ofsmaller precipitates can exhibit greater strength than a similar alloywith larger precipitates. In certain embodiments, the nanoscaleprecipitates can include A₃Zr precipitates having an L1₂-structure in anα-Al (f.c.c.) matrix as well as Al—Zr-Inoculant precipitates.

In certain embodiments, an improved aluminum alloy can be formedpredominantly of aluminum (e.g., about 99% by weight aluminum or more),and small quantities of zirconium and an inoculant. For example,suitable aluminum alloys can include, by weight percentage, about 0.1%to about 0.4% zirconium, and about 0.01% to about 0.2% of an inoculant,with the remainder of the aluminum alloy being aluminum and tracequantities of additional elements. Such trace elements can form about 1%or less of the aluminum alloy. For example, one or more of iron,silicon, copper, manganese, magnesium, chromium, zinc, titanium, boron,gallium, vanadium, nickel, antimony, scandium or other elements can befound, or included, in certain aluminum alloys. In certain embodimentsincluding such other elements or impurities, iron can be included atabout 0.3% to about 0.7%, by weight percentage; silicon can be includedat about 0.06% or less, by weight percentage; copper can be included atabout 0.007% or less, by weight percentage; manganese can be included atabout 0.005% or less, by weight percentage; magnesium can be included atabout 0.015% or less, by weight percentage; chromium can be included atabout 0.002% or less, by weight percentage; zinc can be included atabout 0.04% or less, by weight percentage; titanium can be included atabout 0.008% or less, by weight percentage; boron can be included atabout 0.001% to about 0.006% by weight percentage; gallium can beincluded at about 0.03% or less, by weight percentage; vanadium can beincluded at about 0.004% or less, by weight percentage; nickel can beincluded at about 0.03% or less by weight percentage; and any othertrace elements can be included at about 0.03% or less individually or atabout 0.1% collectively, by weight percentage. Aluminum, zirconium, andan inoculant can constitute the remainder of such aluminum alloys.

In comparison to other known aluminum-zirconium alloys having nanoscalealuminum-zirconium precipitates, the inclusion of an inoculant into thealuminum-zirconium alloy can allow for a reduction in the duration ofvarious heat aging steps used to promote precipitation. For example, theinclusion of tin as an inoculant in an aluminum-zirconium alloy canallow for heat aging steps to have a total duration of about 24 hours orless in certain embodiments, about 12 hours or less in certainembodiments; or about 8 hours or less in certain embodiments.Additionally, the inclusion of an inoculant into an aluminum-zirconiumalloy can also promote the formation of precipitates having a smallerdiameter than comparable precipitates formed on aluminum-zirconiumalloys formed without such an inoculant. Other benefits can also beobserved due to the inclusion of an inoculant. For example, wire samplesformed of an aluminum-zirconium alloy free of an inoculant can becomeprogressively weaker over the duration of a heat aging protocol. Similarsamples including such an inoculant can conversely become stronger overthe duration of a heat aging protocol. This difference in strengthbetween the two samples is believed to have been caused by the inabilityof the inoculant-free aluminum-zirconium alloy sample to produceprecipitates as small as the precipitates found in the aluminum alloyhaving zirconium and an inoculant.

The nanoscale precipitates of an aluminum alloy including both zirconiumand an inoculant can have an average diameter of about 100 nanometers(“nm”) or less, in certain embodiments; an average diameter of about 20nm or less, in certain embodiments; an average diameter of about 10 nmor less, in certain embodiments; or an average diameter of about 3 nm toabout 7 nm in certain embodiments. As can be appreciated, such averagediameters can offer a number of benefits over aluminum alloys havinglarger precipitates. For example, smaller precipitates can lead toimproved strength and heat/creep resistance while maintaining goodelectrical properties and ductility. These properties can also beenhanced by a high density of precipitates. In certain embodiments, thenanoscale precipitates can be found in a high number density on thealuminum-zirconium alloy and can have, for example, a number density ofabout 10²¹ nanoscale precipitates per m³, or greater.

In certain embodiments, an improved aluminum-zirconium alloy can includeiron. Iron, in suitable quantities, can form beneficial microscalechannels on the alloy. For example, about 0.3% to about 0.7% iron cancause the formation of microscale channels in an aluminum-zirconiumalloy including an inoculant. Such microscale channels, in combinationwith the nanoscale precipitates, can form beneficial hierarchicalmicrostructures.

For example, Al_(99%)F_(0.55%)Zr_(0.34%)Sn_(0.1%) exhibits ahierarchical microstructure that is highly resistant to creep as aresult of Al—Fe intermetallic channels and regions of both high and lowdensity Al—Zr—Sn nanoscale precipitates. Such microstructures defined bythe plurality of nanoscale precipitates and channels can allow thealuminum-zirconium alloy to maintain strength over longer periods oftime, even at relatively higher temperatures. For example, analuminum-zirconium alloy cable formed with such microstructures heatedto 280° C. for about 1 hour can retain a tensile strength greater than90% of the original temperature tensile strength before the heatresistance testing when measured in accordance to ASTM B941.

As can be appreciated, the formation of microstructures with nanoscaleprecipitates on an aluminum-zirconium alloy can also permit thealuminum-zirconium alloy to exhibit various improvements to itsmechanical and electrical properties. For example, an aluminum-zirconiumalloy including small quantities of an inoculant can, in certainembodiments, exhibit an elongation at break greater than 14.5%, anultimate tensile strength (“UTS”), after heat aging at about 450° C. for48 hours, of about 140 MPa or more in certain embodiments, about 130 MPaor more in certain embodiments, and of about 120 MPa or more in certainembodiments. The aluminum-zirconium alloy can exhibit an electricalconductivity compared to copper of about 56% or more as measured inaccordance to the International Annealed Copper Standard (“IACS”).

Additionally, in certain embodiments, improved aluminum-zirconium alloysdescribed herein can exhibit substantially improved creep performance ascompared to similar aluminum alloys without the nanoscale precipitates.As can be appreciated, improved creep performance can facilitate the useof such improved aluminum-zirconium alloys in applications that werepreviously difficult for pure aluminum or known aluminum alloys to beutilized in.

An improved aluminum-zirconium alloy as described herein can alsoexhibit improved resistance to stress relaxation resistance. As can beappreciated, stress relaxation is one of the most important concerns inthe design of electrical contacts and is defined as the decrease instress when subject to a constant strain. A conductive element (e.g.,wire) formed of improved aluminum-zirconium alloy,Al_(99%)Fe_((0.4-0.5)%)Zr_((0.25-0.3)%)Sn_((0.05-0.1)%) for example, canexhibit a stress relaxation time to reach about 85% of an initial stressthat is about 2 times longer in duration than an aluminum-zirconiumalloy formed without an inoculant when measured in accordance to ASTME328 standards. Both conductive elements were initially stressed to 75%of their respective yield strength values. As can be appreciated,improved resistance to stress relaxation can allow for stronger cablesthat resist deformation or improved electrical connectors.

In addition to improved stress relaxation resistances, an improvedaluminum-zirconium alloy can also exhibit about 40% higher yield stressthan a comparative 8000 series aluminum alloy for example, as describedby, ASTM Specification 13800 and having chemical formulaAlFe_(0.430%)Zn_(0.20%)Si_(0.40%). As can be appreciated, suchimprovements to the yield strength and stress relaxation time can allowfor the improved aluminum-zirconium alloy to better withstand highercrimping or terminating forces.

According to certain embodiments, improved aluminum-zirconium alloysdescribed herein can be formed into a conductive element of anelectrical cable through one or more wire processing steps. For example,in certain embodiments, the process of producing a conductive elementcan include the steps of casting an as-cast shape (e.g., a bar), hotrolling the as-cast shape into a redraw rod, and then drawing the redrawrod into a conductive element, such as a wire. This process can beperformed continuously.

In certain embodiments, an as-cast shape of an improvedaluminum-zirconium alloy can be cast using any known casting method. Forexample, an Al_(99%)Fe_((0.4-0.5)%)Zr_((0.25-0.3)%)Sn_((0.05-0.1)%)alloy can be cast by melting the alloy in air at about 800° C. andcontinuously casting the as-cast shape. As will be appreciated, othercasting techniques can be used as known in the art. In certainembodiments, an as-cast shape can subsequently be worked or furtherformed into a redraw rod using hot rolling techniques prior to wiredrawing. As illustration only, a suitable diameter for a redraw rod canbe about 0.375″ inches in diameter.

The re-draw rod can undergo a wire drawing process to produce aconductive wire or element. Generally, a cold wire drawing process canbe utilized to produce wires having excellent electrical and mechanicalproperties. As can be appreciated, the diameter of the conductive wirecan be selected depending upon the electrical and mechanical propertiesnecessary for any specific cabling application. For example, aconductive wire intended for an overhead conductor cable can berelatively thick in diameter while conductive wires for smallerapplications can be thinner. In certain embodiments, more than one wiredrawing step can also be used to produce a particularly high gauge(small diameter) wire. As known in the art, it is also possible toproduce conductive elements having non-circular cross-sectional shapesthrough known wire drawing and other forming techniques.

In certain embodiments, the formation of nanoscale precipitates on animproved aluminum-zirconium alloy can be enhanced through the use ofcertain additional steps during the wire processing operations. Theadditional steps can generally include various heat treatment processessuch as peak aging and annealing processes. Heat treatment andsubsequent cooling can promote precipitation of the nanoscaleprecipitates. As can be appreciated, the additional steps can alsoimprove the mechanical and electrical properties of thealuminum-zirconium alloy. Advantageously, the heat treatment steps usedto promote the precipitation of the present nanoscale precipitates canbe shorter in duration and can be performed at lower temperatures thanknown comparable heat treatment applications for other conventionalaluminum alloys.

A peak aging step (sometimes referred to as precipitation hardeningprocess) can generally refer to the use of elevated heat to produce fineparticles of a second phase in an alloy. In the case of the improvedaluminum-zirconium alloys described herein, the desired nanoscaleprecipitates can be formed during peak aging. Peak aging can beperformed as a stand-alone heat treatment on a redraw rod, or combinedwith the annealing step of an intermediate or finished drawn wire. Peakaging can be conducted with any suitable heating system such asresistance furnace, induction furnace, or gas-fired furnace. For analuminum-zirconium alloy formed ofAl_(99%)Fe_((0.4-0.5)%)Zr_((0.25-0.3)%)Sn_((0.05-0.1)%), a peak agingprocess can involve heating the redraw rod after hot rolling to anelevated temperature between about 400° C. to about 450° C. in certainembodiments, and between about 425° C. to about 450° C. in certainembodiments. The duration of a peak aging step can be about 24 hours toabout 48 hours in certain embodiments and about 24 hours in certainembodiments. In certain embodiments, peak aging of a redraw rod canslightly increase the tensile strength at lower aging temperatures orslightly decrease the tensile strength at higher aging temperatures andcan increase the conductivity from about 52% IACS to about 58% IACS.

According to certain embodiments, a peak aging step can be combined withan annealing step of an intermediate, or finished, drawn wire. Thecombination of a peak aging step and an annealing step into a singlestep can promote the formation of nanoscale precipitates while alsoacting to improve ductility, lower strength and/or hardness, and recoverconductivity lost during work-hardening that can occur during a wiredrawing process. The combined annealing and peak aging step can occur inair. In certain embodiments, a combined peak aging and annealing stepcan occur at a temperature between about 300° C. to about 450° C. for aduration between about 3 hours and about 24 hours. In certainembodiments, an annealing step can be performed following wire drawingafter peak aging of a redraw rod. In such embodiments, the anncalingstep can be used to improve ductility, lower strength and/or hardness,and recover conductivity lost during work-hardening that occurs duringthe wire drawing process. The optional step of peak aging can influenceboth the temperature and duration of any annealing step. For example, ifa peak aging process is performed on a redraw rod, a later annealingstep can occur at a lower temperature and/or for a shorter duration oftime than a wire annealed without a peak aging step. For example, anAl_(99%)Fe_((0.4-0.5)%)Zr_((0.25-0.3)%)Sn_((0.05-0.1)%) conductive wireundergoing both peak aging and annealing can use a temperature betweenabout 300° C. and about 400° C. for the annealing step instead of atemperature greater than 400° C. used in a comparable cable having acombined annealing and peak aging step. As can be appreciated, ifmultiple wire drawing steps are performed, an annealing process can beperformed after each such step to improve ductility, lower strengthand/or hardness, and recover conductivity lost during work-hardeningthat occurs during such wire drawing processes.

A non-limiting example of a suitable wire drawing process is disclosed.In the example wire drawing process, a trapezoidal as-cast bar with anabout 5.75 in² cross-sectional area can be continuously cast. Thetrapezoidal as-cast bar can then be rot rolled into a 0.375″ redraw rod.The 0.375″ redraw rod can be peak-aged for about 48 hours at about 420°C. to form suitable nanoscale precipitates before wire drawing to a 1.6mm (0.063″) intermediate wire. The as-drawn 1.6 mm intermediate wire canthen be annealed for about 6 hours at about 400° C. to improve ductilityrequired for further wire drawing. The intermediate wire can then bewire drawn to an about 0.3 mm (0.0118″) diameter wire. The as-drawn 0.3mm wire can subsequently be annealed to further improve ductility, lowerstrength and/or hardness, and recover conductivity lost duringwork-hardening associated with the final wire drawing step.

Additional details about suitable aluminum-zirconium alloys and heattreatment steps are disclosed in U.S. Patent App. Publication No.2015/0259773 A1 which is hereby incorporated by reference in itsentirety.

Cables including conductive elements formed from the improvedaluminum-zirconium alloys described herein can be used in a variety ofapplications including, for example, automotive applications, aerospaceapplications, power transmission applications, household cablingapplications, and any other application requiring a lightweight cable.For example, improved aluminum-zirconium alloys described herein can beparticularly useful as a power cable in automotive and aerospace powersystems including for example, as a battery wire in an electricallypowered vehicle. Conductive elements formed from an improvedaluminum-zirconium alloy as disclosed herein can be used in wires assmall as about 1 μm in diameter in certain embodiments or as large asabout 1″ in diameter in certain embodiments. For example, aluminum bondwires as small as about 18 μm (0.7 mils) in diameter can be formed incertain embodiments and wire as large as about 4/0 (0.46″ or 11.68 mmm)in diameter can be formed in certain embodiments.

Generally, the present aluminum-zirconium alloy conductive wires orelements can be utilized similarly to conductive wires or elementsproduced from known aluminum alloys such as heat resistantaluminum-zirconium alloys and 8000 series aluminum alloys. Certainconventional examples of heat resistant aluminum-zirconium alloys aredescribed in ASTM Specification B941 and can have, for example, thechemical formula AlZr_(0.287)% Fe_(0.205%)Si_(0.045%). As will beappreciated however, the improved creep resistance and stress relaxationresistance of the improved aluminum-zirconium alloys described hereincan allow for improved performance of the cables as well as new uses.

Cables including conductive elements formed of the improvedaluminum-zirconium alloys described herein can generally be constructedusing known techniques and cable geometries by replacing the existingconductive elements with the conductive element formed from the improvedaluminum-zirconium alloy. For example, simple power cables can be formedby stranding aluminum-zirconium alloy conductive elements and thencoating the conductive elements with an insulation layer and/or jacketlayer. Any known insulation layer or jacket layer can be utilized asknown in the art.

In certain embodiments, conductive elements formed of an improvedaluminum-zirconium alloy described herein can be included in overheadconductor cables. As can be appreciated, overhead conductors can beformed in a variety of configurations including aluminum conductor steelreinforced (“ACSR”) cables, aluminum conductor steel supported (“ACSS”)cables, aluminum conductor composite core (“ACCC”) cables and allaluminum alloy conductor (“AAAC”) cables. ACSR cables are high-strengthstranded conductors and include outer conductive strands, and supportivecenter strands. The outer conductive strands can be formed from theimproved aluminum-zirconium alloys described herein. The centersupportive strands can be steel and can have the strength required tosupport the more ductile outer conductive strands. ACSR cables can havean overall high tensile strength. ACSS cables areconcentric-lay-stranded cables and include a central core of steelaround which is stranded one, or more, layers of the improvedaluminum-zirconium alloy wires. ACCC cables, in contrast, are reinforcedby a central core formed from one, or more, of carbon, glass fiber, orpolymer materials. A composite core can offer a variety of advantagesover an all-aluminum or steel-reinforced conventional cable as thecomposite core's combination of high tensile strength and low thermalsag enables longer spans. ACCC cables can enable new lines to be builtwith fewer supporting structures. AAAC cables can be made with theimproved aluminum-zirconium alloy wires. ACSR, ACSS, ACCC, and AAACcables can be used as overhead cables for overhead distribution andtransmission lines.

Composite core conductors are useful due to having lower sag at higheroperating temperatures and their higher strength to weight ratio.Non-limiting examples of composite cores can be found in U.S. Pat. Nos.7,015,395, 7,438,971, 7,752,754, U.S. Patent App. No. 2012/0186851, U.S.Pat. Nos. 8,371,028, 7,683,262, and U.S. Patent App. No. 2012/0261158,each of which are incorporated herein by reference.

Beneficial properties of the improved aluminum-zirconium alloysdescribed herein can also facilitate the formation of bonding wires fromthe described alloys. As can be appreciated, bonding wires are used tofacilitate the electrical interconnection of one or more componentsacross relatively short distances. For example, boding wires can be usedfor the interconnection of a microprocessor (microelectronic device) toa microprocessor package or printed circuit board, a battery cell toanother battery cell, or can be used in down-hole drilling electronics.Suitable bonding wires are formed of metals and metal alloys whichexhibit a variety of useful properties such as good bonding strength tosubstrates, and resistance to heat, fatigue, and creep. The improvedaluminum-zirconium alloys described herein can exhibit a good balance ofthese properties and wires formed of the improved alloys can exhibitbetter endurance performance than wires formed of pure aluminum.

For example, bonding wires formed of the aluminum-zirconium alloysdescribed herein can demonstrate good results when tested according tothe heat aging processes described in ASTM B941, can resist fatiguefailure for at least about 10⁶ cycles at 85 MPa of applied stress whentested in accordance to ASTM E466, and can exhibit a creep rate of about50% an hour or less when subjected to 50 MPa of applied stress at atemperature of 185° C. when tested in accordance to ASTM E139. Incertain embodiments, the described bonding wires can resist fatiguefailure for at least about 10⁷ cycles at 85 MPa of applied stress whentested in accordance to ASTM E466. In certain embodiments, the describedbonding wires can exhibit a creep rate of about 25% an hour or less whensubjected to 50 MPa of applied stress at a temperature of 185° C. whentested in accordance to ASTM E139 and, in certain embodiments, canexhibit a creep rate of about 15% an hour or less.

The ASTM B941 standard provides guidance on sample preparation and heataging testing protocol for heat resistant aluminum-zirconium roundwires. Aluminum-zirconium cables described herein demonstrated anultimate tensile strength value after heat aging for 1 hour at 280° C.of about 90% or more of the unaged ultimate tensile strength value whentested in accordance to ASTM B941. In certain embodiments, about 95% ormore of the unaged ultimate tensile strength was retained. In certainembodiments, about 99% or more of the ultimate tensile strength wasretained.

EXAMPLES

Table 1 depicts the compositions of several Example aluminum alloys.Comparative Examples 1 and 2 are 8000 series aluminum alloy and heatresistant aluminum-zirconium alloy respectively. Inventive Examples 3and 4 depict aluminum-zirconium alloys including a tin inoculant. TheExample aluminum alloys depicted in Table 1 were processed into wires toevaluate various physical and electrical properties exhibited by thealloys.

TABLE 1 Al and Other Elements Unavoidable Alloy Fe Zr Sn Si Zn Ti Ga VImpurities Comparative 0.430% — — 0.040% 0.020% 0.01% 0.01% — RemainderExample 1 (8000 series aluminum alloy) Comparative 0.206% 0.287% —0.045% 0.010% 0.01% 0.01% 0.01% Remainder Example 2 (Heat resistantaluminum- zirconium alloy Inventive 0.430% 0.300% 0.100% 0.040% 0.020% —— — Remainder Example 3 Inventive 0.431% 0.266% 0.072% 0.043%  0.01%0.01% 0.01% 0.01% Remainder Example 4

Table 2 depicts the results of testing 3.175 mm wires formed of thealuminum alloys of Comparative Example 1 and Inventive Example 3. Thewires of each Example aluminum alloy were evaluated for elongation atbreak, ultimate tensile strength (“UTS”), conductivity, and stressrelaxation at room temperature. Stress relaxation time was measured inaccordance with ASTM E328.

TABLE 2 Elonga- Conductivity Stress tion UTS at 20° C. Relaxation ID (%)(MPa) (% IACS) Time* (hours)) Comparative 12-16  94-117 62.0-62.6 2.7(85% of Example 1 initial stress) 15.1 (80% of initial stress) Inventive14.9-15.7 140-142 58.2-60.4 5.5 (85% of Example 3 initial stress) 59.7(80% of initial stress)

As depicted in Table 2 and FIG. 1, the wires formed of the alloy ofInventive Example 3 exhibits superior ultimate tensile strength andstress relaxation compared to the wires formed of the aluminum alloy ofComparative Example 1.

FIG. 1 further depicts the room temperature stress relaxation results ofthe wires formed of Comparative Examples 1 and Inventive Example 3evaluated in Table 2. As illustrated by FIG. 1, the wires formed ofInventive Example 3 take about twice as long as the wires formed ofComparative Example 1 to relax to 85% of the initial stress (5.5 hourscompared to 2.7 hours). The initial stress was set at 75% of the yieldstress in each case. This difference in stress relaxation time increaseswith increasing time. For example, the wires formed of Inventive Example3 take about 4 times as long as the wires formed of Comparative Example1 to relax to 80% of the initial stress (extrapolated to 59.7 hourscompared to 15.1 hours).

Table 3 depicts the heat aging performance of 9.525 mm redraw rodsformed from the aluminum alloys of Comparative Example 2 and InventiveExample 4. The heat aging performance details the UTS and IACSconductivity of the redraw rods after heat aging at temperatures ofabout 400° C. for 8 hours, 24 hours, and 48 hours. Ultimate tensilestrength was determined by measuring the Vickers hardness in accordanceto ASTM E92 and then correlating the ultimate tensile strength from theVickers hardness value by multiplying by about ⅓.

TABLE 3 Aging UTS (MPa) Conductivity at 20° C. (% ACS) Time ComparativeInventive % Comparative Inventive % (hours) Example 2 Example 4Different Example 2 Example 4 Different 0 137 155 12.6 52.4 50.4 −3.8 8124 145 16.7 55.3 53.3 −3.6 24 136 164 20.6 56.2 55.6 −1.1 48 125 16329.8 57.7 57.2 0.0 % −8.7 5.2 10.1 13.5 Improvement/ drop after 48 hours

As depicted in Table 3, redraw rods formed of the aluminum alloys ofInventive Example 4 exhibit improved properties after heat aging and theredraw rods match or exceed the properties of the redraw rods formedfrom the aluminum alloys of Comparative Example 2. For example, theredraw rods formed of the aluminum alloy of Inventive Example 4 exhibita superior UTS both in absolute values as well as improvement after heataging. The redraw rods formed of Inventive Example 4 also match the IACSconductivity of the redraw rods formed from the aluminum alloy ofComparative Example 2 after heat aging for 48 hours.

Isochronal Aging Performance

Table 4 depicts the shift in peak aging properties for 38.1 mm (1.5″)as-cast rods formed from the aluminum alloys of Comparative Example 5and Inventive Example 6 after heat aging for a constant time. Theas-cast rods formed from Comparative Example 5 and Inventive Example 6differ in their inclusion of a tin inoculant. The aluminum alloy ofComparative Example 5 is AlFe_(0.55)Zr_(0.34) while the aluminum alloyof Inventive Example 6 is AlFe_(0.55)Zr_(0.34)Sn_(0.1). Ultimate tensilestrength was determined by measuring the Vickers hardness in accordanceto ASTM E92 and then correlating the ultimate tensile strength from theVickers hardness value by multiplying by about ⅓.

TABLE 4 Comparative Inventive Example 5 Example 6 Peak Aging Temperature(° C.) 475 430 UTS (MPa) Initial 92 110 At peak aging temperature 153165 Conductivity (% IACS) Initial 50 51.5 At peak aging temperature 5757.5

As depicted by Table 4, the as-cast rods formed of Inventive Example 6exhibit a higher initial UTS before heat aging (110 MPa vs 92 MPa), ahigher peak UTS after heat aging (165 MPa vs 153 MPa), and achieve thepeak UTS at a lower heat aging temperature than the as-cast rods formedof Comparative Example 5 (430° C. vs. 475° C.). The as-cast rods formedof Inventive Example 6 exhibit a 50.0% increase in UTS after heat aging.Similar trends are also seen for the conductivity of as-cast rods formedof Inventive Example 6.

Constant Temperature Aging Performance

Table 5 depicts the UTS and conductivity of an as-cast 38.1 mm (1.5″)rod formed of the alloys of Comparative Example 5 and Inventive Example6 after undergoing heat aging at a constant temperature of 450° C. Asillustrated by Table 5, the as-cast rods formed of Inventive Example 6exhibit a higher initial UTS and conductivity than the as-cast rodsformed of Comparative Example 5 and achieves these benefits with ashorter heat aging duration. After heat aging, the as-cast rods formedof Inventive Example 6 exhibit a 30.4% increase in UTS. Ultimate tensilestrength was determined by measuring the Vickers hardness in accordanceto ASTM E92 and then correlating the ultimate tensile strength from theVickers hardness value by multiplying by about ⅓.

TABLE 5 Comparative Inventive Example 5 Example 6 Peak Aging Time 80hours 30 hours UTS (MPa) Initial 87 115 At Peak Aging Time 127 150Conductivity (% IACS) Initial 49 51.5 At Peak Aging Temperature 59 59.5

Table 6 depicts the effect of tin on UTS & conductivity of 9.5 mm redrawrods after heat aging at 400° C. for several periods of time. Table 6includes redraw rods formed of Comparative Example 7 and InventiveExample 8. The aluminum alloy of Comparative Example 7 isAlFe_(0.43)Zr_(0.3) and the aluminum alloy of Inventive Example 8 isAlFe_(0.43)Zr_(0.3)Sn_(0.072). Ultimate tensile strength was determinedby measuring the Vickers hardness in accordance to ASTM E92 and thencorrelating the ultimate tensile strength from the Vickers hardnessvalue by multiplying by about ⅓.

TABLE 6 Aging UTS (MPa) Conductivity at 20° C. (% ACS) Time ComparativeInventive % Comparative Inventive % (hours) Example 2 Example 4Different Example 2 Example 4 Different 0 156 169 8.3 53.7 50.6 −5.8 8136 158 16.1 55.6 53.4 −3.9 24 135 179 17.0 56.7 55.6 −1.9 48 138 17829.0 57.2 37.3 +0.2 % −11.6 5.3 6.5 13.2 Improvement/ drop after 48hours

As depicted by Table 6, the redraw rods of Inventive Example 8,including 0.072% tin, enabled a UTS peak to occur after about 24 hoursof heat aging. The redraw rods of Comparative Example 7, formed withouttin, had a UTS peak occur only after 48 hours of heat aging.Furthermore, the addition of 0.072% tin increased the UTS by about 29%after 48 hours of aging, with only minor changes in the electricalconductivity.

Table 7 depicts the elongation at break, ultimate tensile strength,conductivity, and creep of 0.3 mm diameter bonding wires formed of purealuminum (99.99% Al minimum and labeled as Comparative Example 9), andfrom the aluminum alloy of Inventive Example 4. As illustrated by Table7, the wires formed of Inventive Example 4 exhibit improved UTS,elongation at break, and a creep rate at 185° C. that is about 21 timesor more slower than the creep rate of wires formed of 99.99% purealuminum at an applied stress of 30 to 70 MPa when measured inaccordance to ASTM E139.

TABLE 7 Elonga- Conductivity tion UTS at 20 C. Creep Rate at Example (%)(MPa) (% IACS) 185° C. (%/hr) Comparative 11.4 103.8 63.5 7 (30 MPaExample 9 Applied Stress) (Pure Aluminum) 210 (50 MPa Applied Stress)2500 (70 MPa Applied Stress) Inventive 12.4 110 59.9 0 (30 MPa Example 4Applied Stress) 10 (50 MPa Applied Stress) 110 (70 MPa Applied Stress)

As depicted in Table 8, additional bonding wire performance wasevaluated using wires formed of 99.99% pure aluminum (ComparativeExample 9) and the aluminum alloy of Inventive Example 4. The wiresformed of Comparative Example 9 were 380 μm in diameter while the wiresformed of Inventive Example 4 were 392 μm in diameter.

TABLE 8 UTS Conductivity at 20 C. Example (MPa) (% IACS) ComparativeExample 9 — 64.6 (Pure Aluminum)- 380 μm wire Inventive Example 4- 392μm 88.9 59.0 wire

Heat Aging Performance

Table 9 depicts the UTS of 300 μm diameter wires formed from thealuminum alloy of Inventive Example 4 and 99.99% pure aluminum(Comparative Example 9) after heat aging at 300° C. As illustrated byTable 9, the wires formed of Inventive Example 4 exhibit a UTS drop ofabout 4% after heat aging for 24 hours while the wires formed of purealuminum exhibit a UTS drop of about 25%. Ultimate tensile strength wasdetermined by measuring the Vickers hardness in accordance to ASTM E92and then correlating the ultimate tensile strength from the Vickershardness value by multiplying by about ⅓.

TABLE 9 Comparative Ultimate Tensile Strength Inventive Example 9 (MPa)after Heat Aging for: Example 4 (Pure Aluminum) Initial 111.0 95.1 2hours 106.2 73.1 5 hours 106.9 71.0 24 hours  106.2 71.7

The 300 μm diameter wires formed of Inventive Example 4 alsodemonstrated excellent results when tested in accordance to ASTM B941heat resistance standards. The ASTM B941 standard describes heat agingof a sample at 280° C. for 1 hour and then cooling the sample to roomtemperature. The 300 μm wires formed of Inventive Example 4 retainedgreater than 99% of the room temperature UTS when tested in accordanceto ASTM B941.

Fatigue Performance

FIG. 2 depicts the room temperature fatigue properties of 1.6 mm wireformed from the aluminum alloys of Comparative Example 1 and InventiveExample 4. As depicted by FIG. 2, the wires formed from the aluminumalloy of Inventive Example 4 exhibited superior fatigue performancecompared to the wires formed from the aluminum alloy of ComparativeExample 1 when tested in accordance to ASTM E466.

Bond Performance for Bonding Wire Applications

An industrial heavy-aluminum wire wedge bonding machine (HesseMechatronics BJ939) was used to assess the bonding performance ofbonding wires formed of the Example aluminum alloys. The performance wasevaluated assessing about 1000 bonds made with a 2-step ultrasonicvoltage application. Bonding performance of wires formed of the aluminumalloy of Inventive Example 4 were found to match or exceed theperformance of identical wires formed of pure aluminum and other typicalaluminum bonding wire alloys (such as Al-1% Si & Al—Mg). The wiresformed of Inventive Example 4 did not exhibit any bond failures(including any heel cracks, abnormal tail lengths, bond ears, ordeformed areas) with proper setting of relevant bond parameters(ultrasonic power, bonding force, ultrasonic duration, and loop height).Furthermore, the bonds performed very well in standard pull tests andshear tests. For example, bonds made with 387 μm wire formed ofInventive Example 4 survived a 1000 cN pull test conducted in accordanceto ASTM F459 and greater than a 2500 gram-force in a 20 mil (0.508 mm)shear test conducted in accordance JESD22-B116A. The results of theshear test are depicted in FIG. 3.

It should be understood that every maximum numerical limitation giventhroughout this specification includes every lower numerical limitation,as if such lower numerical limitations were expressly written herein.Every minimum numerical limitation given throughout this specificationwill include every higher numerical limitation, as if such highernumerical limitations were expressly written herein. Every numericalrange given throughout this specification will include every narrowernumerical range that falls within such broader numerical range, as ifsuch narrower numerical ranges were all expressly written herein.

Every document cited herein, including any cross-referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests,or discloses any such invention. Further, to the extent that any meaningor definition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in the document shallgovern.

The foregoing description of embodiments and examples has been presentedfor purposes of description. It is not intended to be exhaustive orlimiting to the forms described. Numerous modifications are possible inlight of the above teachings. Some of those modifications have beendiscussed and others will be understood by those skilled in the art. Theembodiments were chosen and described for illustration of ordinary skillin the art. Rather it is hereby intended the scope be defined by theclaims appended various embodiments. The scope is, of course, notlimited to the examples or embodiments set forth herein, but can beemployed in any number of applications and equivalent articles by thoseof hereto.

1.-19. (canceled)
 20. An aluminum alloy comprising: about 0.1% to about1% iron by weight; about 0.1% to about 0.5% zirconium by weight; about0.01% to about 0.2% of an inoculant by weight; and aluminum as theremainder.
 21. The aluminum alloy of claim 20, wherein the inoculantcomprises one or more of tin, indium, antimony, and magnesium.
 22. Thealuminum alloy of claim 20, wherein the inoculant comprises one or moreof zinc, gallium, germanium, lead, arsenic, and bismuth.
 23. Thealuminum alloy of claim 20, wherein the inoculant comprises tin.
 24. Thealuminum alloy of claim 20, wherein the inoculant comprises at least oneGroup 3A, 4A, and 5A metal or metalloid.
 25. The aluminum alloy of claim20, wherein the inoculant comprises about 0.05% to about 0.1% of thealuminum alloy by weight.
 26. The aluminum alloy of claim 20, furthercomprising silicon.
 27. The aluminum alloy of claim 26, wherein thesilicon comprises about 0.01% to about 0.2% of the aluminum alloy byweight.
 28. The aluminum alloy of claim 20, wherein the iron comprisesabout 0.3% to about 0.7% of the aluminum alloy by weight.
 29. Thealuminum alloy of claim 20, wherein the zirconium comprises about 0.2%to about 0.4% of the aluminum alloy by weight.
 30. The aluminum alloy ofclaim 20, comprising a plurality of nanoscale precipitates having anL1₂-structure in an α-Al face centered cubic matrix, the plurality ofprecipitates comprising Al₃Zr precipitates, and the plurality ofprecipitates being present in the aluminum alloy at a density of about10²¹ precipitates per m³ or more.
 31. The aluminum alloy of claim 30,wherein the plurality of precipitates has an average diameter of about20 nm or less.
 32. The aluminum alloy of claim 30, wherein the pluralityof precipitates has an average diameter of about 3 nm to about 7 nm. 33.The aluminum alloy of claim 30, wherein the plurality of precipitatescomprises Al—Zr—X precipitates, X being the inoculant.
 34. The aluminumalloy of claim 20, having an elongation at break greater that 14.5% andan ultimate tensile strength (UTS) of at least about 120 MPa.
 35. Thealuminum alloy of claim 20, having an electrical conductivity comparedto copper of at least about 56% as measured in accordance to theInternational Annealed Copper Standard (IACS).
 36. The aluminum alloy ofclaim 20, having a stress relaxation time to reach about 85% of theinitial stress that is about 2-times longer than a similar alloy withoutinoculant when measured in accordance with ASTM E328 standards.
 37. Thealuminum alloy of claim 20, having about 40% higher yield stress than acomparative 8000-series aluminum alloy described by ASTM SpecificationB800.
 38. The aluminum alloy of claim 20, adapted for use in a castingapplication.
 39. The aluminum alloy of claim 38, wherein the castingapplication is die casting.
 40. A cast aluminum component, comprisingthe aluminum alloy of claim
 20. 41. An aluminum alloy comprising: about0.3% to about 0.7% iron by weight; about 0.2% to about 0.4% zirconium byweight; about 0.05% to about 0.2% of an inoculant by weight, wherein theinoculant comprises tin; and aluminum as the remainder.
 42. The aluminumalloy of claim 41, comprising about 0.25% to about 0.3% zirconium byweight.